Many methods or devices are implemented in the present art, which can arbitrarily be classified into two main categories.
A first category consists of devices or methods which can be qualified as analogical. It is possible for instance to mould the foot shape. The user lays his foot on a block of malleable, silicone-based for instance, material. Because of the exerted pressure, the material block will keep the footprint shape and can be used as a matrix for later production of an orthopaedic shoe or sole.
The precision obtained by this method is not very high. Furthermore, passing the thus acquired matrix to the end product, i.e. the shoe or sole, is neither easy nor quick to perform. The method requires a large number of manual steps.
Furthermore, not only one but generally several footprints need be obtained, in order to optimally simulate various physical states: foot laying (flat), foot resting on the tip, and foot resting on the heel, for instance, which makes the process more complex.
The second category includes digital devices and methods.
Many systems with optical sensors are known, in particular the system disclosed by the applicant's French Patent FR 2 685 764 entitled: "Capteur optique compact et a haute resolution pour l'analyse de formes tri-dimensionnelles", i.e. "A compact, high resolution optical sensor for analyzing tri-dimensional shapes". That system allows acquiring tri-dimensional pieces having a warped surface and digitizing them. For that purpose, the system includes an optical sensor with a laser beam source and one or more cameras analyzing the trace formed by the laser beam on the object to be studied.
Stating it more precisely, the system generates a so-called laser "plane", i.e. a very thin sectoral lamellar beam with a width that allows it to cover either all or part of the object to be analyzed, with the above cameras observing the beam trace under different incidence angles. Acquisition and digitalization are performed by scanning the object surface by the laser light plane.
In the case of the applications aimed at by the invention, such an optical sensor system cannot be used as it is for acquiring and digitalizing the profile of a foot arch, mainly because the surface the profile of which is to be plotted is located underneath the foot, and therefore cannot be accessed to, inasmuch as it should be observed while the patient is standing or walking.
That precludes taking full profit from the advantages the optical sensing devices can exhibit on the other hand, through allowing to reach a high resolution in the three-dimensional profile made to a set of points, or does, with known coordinates with respect to a referential (usually a horizontal plane), and through ensuring a rapid acquisition with a high precision, as well as through performing the digitalization of the acquired shape, which allows an immediately or delayed exploitation of the obtained measurements. Namely, the acquired data can be processed by a computer with a pre-recorded program for delivery to an exploiting device (digital control machine tool for instance), and/or viewed, and/or stored in a mass memory for later in situ or remote use.
The obtained result however also depends upon the exact conditions in which the acquisition is performed. The foot namely needs to be in conditions as close to reality as possible. It consequently has to rest on a support surface and the arch of this foot should not be deformed by this support surface, since such would falsify the measurements. The acquisition must be performed from below, i.e. in a practical manner through a transparent wall, for instance a thick glass wall. The foot clearly may not move, once it rests on the transparent support surface. Obtaining the above mentioned scanning therefore requires the beam to be moved with respect to the foot, either by deflection or by a physical movement of the sensor (translation motion).
The presence of a wall, even a transparent one, is not without inconveniences since it will produce deviations (by refraction) of the generated beam or beams, when crossing back and forth (after reflection on the surface of the foot arch). Furthermore, the transparent material may include impurities inducing stray deviations and/or diffraction during scanning. Finally, since the acquisition must be performed in conditions as close to reality as possible, the wall may not be planar, it should simulate the internal shoe surface, which introduces deformations of the generated beam or beams, which will vary during this scanning process.
To solve the above stated problems, the applicant has proposed, in a French patent published under number 2735859 entitled "Procede d'acquisition et de numerisation d'objets au travers d'une paroi transparente et systeme de mise en oeuvre d'un tel procede", i.e. "A method for acquiring and digitalizing objects through a transparent wall and system for implementing such a method", a system comprising several optical sensors surrounding a tri-dimensional object, the shape of which is to be acquired. Each sensor preferably is of a type described in the patent FR-B-2 685 764 and includes a laser source emitting a lamellar planar beam. The set of the laser planes is coplanar, so as to form a single measurement plane. The full shape of the foot can be acquired by successive slices, with each slice being obtained in an almost instantaneous manner, without requiring any rotation of the sensor system around the longitudinal axis of the foot. Acquiring the different slices only needs a translation motion parallel to this axis.
During a preliminary phase, the measurement space is calibrated and the upper and lower surfaces of the transparent wall are acquired and digitized, which allows eliminating the stray influence of this wall (curvature, defects, and so on).
Although this system offers many advantages, and particularly for producing customized shoes, since it allows acquiring and digitizing the full foot shape in just one run, it does not fully meet the needs that appear in the frame of the applications the invention is aiming at, in particular for producing orthopaedic accessories.
Using a transparent wall with a non planar surface, which simulates the internal surface of a shoe, namely only constitutes, at best, a compromise solution. The foot namely rest on a wall with a pre-established shape, whereas only the foot should itself impose a shape to this wall. The shape which should be acquired namely is that of the plantar arch, without any constraint whatsoever. Furthermore, as previously indicated, various positions of the plantar arch should successively be acquired: foot laying (flat), foot resting on the heel and/or on the tip, for instance. A single support shape is not sufficient.
Finally, other requirements are associated with a system used for the preferably considered applications of the invention: simplicity, easy handling, easy transportation of the equipment for plotting the shape of a tri-dimensional object.